Electronic assembly with trenches for underfill material

Abstract

An electronic assembly includes a substrate having bond pads on a surface of the substrate. A solder mask covers the surface of the substrate, and a solder connection is disposed on each of the bond pads. At least one trench is formed in the solder mask, and is located between adjacent ones of the bond pads. At least one component has contact pads, and each contact pad is connected to one of the bond pads via one of the solder connections. The trench is located beneath the device and extends at least from one edge of the device to a location underneath the device. Underfill material fills the trench and space between the solder mask and the device.

1. An electronic assembly comprising:
 a substrate having a plurality of bond pads on a surface of the substrate; 
 a solder mask covering the surface of the substrate; 
 a solder connection on each of the plurality of bond pads; 
 at least one trench formed in the solder mask, the at least one trench located between adjacent ones of the plurality of bond pads; 
 at least one component having a plurality of contact pads, each contact pad connected to one of the plurality of bond pads via one of the solder connections, the at least one trench located beneath the component and extending at least from one edge of the component to a location underneath the component; and 
 underfill material filling the at least one trench and space between the solder mask and the component. 
 
     
     
       2. The electronic assembly of  claim 1 , wherein the at least one trench comprises a plurality of trenches formed in the solder mask, each of the trenches located beneath the component and each of the trenches extends at least from one edge of the at least one component to another edge of the component. 
     
     
       3. The electronic assembly of  claim 1 , further comprising:
 wherein the at least one component includes a plurality of components mounted on the substrate, each of the components having contact pads that are connected to corresponding ones of the bond pads via corresponding ones of the solder connections; 
 wherein the at least one trench includes a plurality of trenches formed in the solder mask, a set of one or more of the trenches located beneath a respective one of the components and each of the trenches in the set extending at least from an edge of the respective component to a location underneath the respective component; and 
 underfill material filling each of the trenches and spaces between the solder mask and each of the components. 
 
     
     
       4. The electronic assembly of  claim 1 , wherein the component is a chip capacitor. 
     
     
       5. The electronic assembly of  claim 1 , wherein the underfill material is dispensed undercoat epoxy that completely fills the space between the solder mask and the component without the formation of micro-voids. 
     
     
       6. The electronic assembly of  claim 1 , wherein a depth of the at least one trench extends partially through the solder mask. 
     
     
       7. The electronic assembly of  claim 1 , further comprising a build-up layer located between the substrate and the solder mask, the at least one trench having a depth extending into the build-up layer. 
     
     
       8. The electronic assembly of  claim 1 , wherein the at least one trench has a depth sufficient to allow dispensed underfill material to flow underneath the component to fill the space between the solder mask and the component. 
     
     
       9. The electronic assembly of  claim 1 , wherein the at least one trench extends a distance past an edge of the component to enable dispensed underfill material to be injected into the trench and thereby flow underneath the component to fill the space between the solder mask and the component. 
     
     
       10. A method of manufacturing an electronic assembly, the method comprising:
 providing a substrate having a plurality of bond pads on a surface of the substrate, a solder mask covering the surface of the substrate, and a solder connection on each of the plurality of bond pads; 
 forming at least one trench in the solder mask, the at least one trench located between adjacent ones of the plurality of bond pads, 
 mounting at least one component on the substrate, the component having a plurality of contact pads, each connected to one of the plurality of bond pads via one of the solder connections, the component being located above the at least one trench and the at least one trench extending at least from one edge of the component to another edge of the component; 
 using the at least one trench, dispensing underfill material to fill space between the solder mask and the component. 
 
     
     
       11. The method of  claim 10 , wherein the forming at least one trench includes forming a plurality of trenches in the solder mask prior to mounting the at least one component on the substrate, each of the trenches located beneath the component and each of the trenches extending at least from one edge of the component to another edge of the component after the component is mounted on the substrate. 
     
     
       12. The method of  claim 10 , further comprising:
 wherein the mounting at least one component includes mounting a plurality of components on the substrate, each of the components having contact pads that are connected to corresponding ones of the bond pads via the solder connections on the bond pads; 
 wherein the forming at least one trench includes forming a plurality of trenches in the solder mask prior to mounting the components on the substrate, at least one of the trenches located beneath each of the components and each of the trenches extending at least from an edge of a respective one of the components to another edge of the respective one of the components; and 
 after the components are mounted on the substrate using the at least one trench beneath each of the components, dispensing underfill material to fill space between the solder mask and each of the components. 
 
     
     
       13. The method of  claim 12 , wherein dispensing underfill material to fill space between the solder mask and each of the components includes using a dispensing needle to individually inject underfill material into the at least one of the trenches located beneath each of the components. 
     
     
       14. The method of  claim 10 , wherein forming at least one trench in the solder mask includes forming at least one trench having a depth sufficient to allow dispensed underfill material to flow underneath the component to fill the space between the solder mask and the component. 
     
     
       15. The method of  claim 10 , wherein forming at least one trench in the solder mask includes forming at least one trench that extends a distance past an edge of the component after the component is mounted on the substrate to enable dispensed underfill material to be injected into the trench and thereby flow underneath the component to fill the space between the solder mask and the component. 
     
     
       16. The method of  claim 10 , wherein the component is a chip capacitor. 
     
     
       17. The method of  claim 10 , wherein the underfill material is undercoat epoxy, and wherein dispensing underfill material to fill space between the solder mask and the component includes dispensing the undercoat epoxy to completely fill the space between the solder mask and the component without the formation of micro-voids. 
     
     
       18. An electronic assembly comprising:
 a substrate having at least two bond pads on a first surface of the substrate; 
 a solder mask on the first surface of the substrate, wherein the solder mask has at least one trench formed therein and extending between the at least two bond pads; 
 a chip capacitor having at least two contact pads that are soldered to the at least two bond pads, respectively; and 
 underfill material filling the at least one trench and a void between the solder mask and the component. 
 
     
     
       19. The electronic assembly of  claim 18 , wherein a depth of the at least one trench extends partially through the solder mask. 
     
     
       20. The electronic assembly of  claim 18 , wherein the at least one trench extends a distance past an edge of the chip capacitor to enable dispensed underfill material to be injected into the trench and thereby flow underneath the chip capacitor to fill the space between the solder mask and the chip capacitor.